Security for electronic messages can be considered to relate to two categories: a privacy category; and an authentication category. For privacy, a sending party may encrypt a message with a key or a passphrase. To decrypt the message, the receiver must use a corresponding key or the passphrase. Such a scheme works best when only those who the sending party trusts have access to the corresponding key or the passphrase. For authentication, the sending party may use a key to generate a signature for a message and send the signature in conjunction with the message. The receiver can use a corresponding key to decrypt the received signature and compare the decrypted signature to a further signature generated using the received message. A match between the decrypted received signature and the further signature can provide the receiving party with confidence that the message originated with the specific sending party.